Editing Ramachandran plot (section)

==Amino-acid preferences==
One might expect that larger side chains would result in more restrictions and consequently a smaller allowable region in the Ramachandran plot, but the effect of side chains is small.<ref name="chak2001">{{cite journal |last1=Chakrabarti |first1=Pinak |last2=Pal |first2=Debnath |year=2001 |title= The interrelationships of side-chain and main-chain conformations in proteins |journal=Progress in Biophysics and Molecular Biology |volume=76 |pages=1–102 |doi=10.1016/S0079-6107(01)00005-0 |issue=1–2 |pmid=11389934|doi-access=free }}</ref> In practice, the major effect seen is that of the presence or absence of the methylene group at Cβ.<ref name="chak2001" /> [[Glycine]] has only a hydrogen atom for its side chain, with a much smaller [[van der Waals radius]] than the CH<sub>3</sub>, CH<sub>2</sub>, or CH group that starts the side chain of all other amino acids. Hence it is least restricted, and this is apparent in the Ramachandran plot for glycine (see Gly plot in [[#Gallery|gallery]]) for which the allowable area is considerably larger. In contrast, the Ramachandran plot for [[proline]], with its 5-membered-ring side chain connecting Cα to backbone N, shows a limited number of possible combinations of ψ and φ (see Pro plot in [[#Gallery|gallery]]). The residue preceding proline ("pre-proline") also has limited combinations compared to the general case.